Fuel Pressure Regulator Bypass: How Much Fuel Can Escape?

A fuel pressure regulator is an important component of a vehicle's fuel system, responsible for maintaining the correct fuel pressure to optimise engine performance, fuel efficiency, and emissions control. There are two main types of fuel pressure regulators: return-style (or bypass) and returnless-style (or blocking-style). The former uses a spring and diaphragm mechanism to control fuel pressure, while the latter does not circulate fuel back to the fuel tank and lacks a return line. Return-style regulators are generally recommended for most EFI installations and carbureted installations with high-pressure pumps. They help keep fuel temperature within operating conditions and allow high-pressure pumps to operate at maximum efficiency. However, they increase system complexity due to the requirement of a return line. On the other hand, deadhead or blocking-style regulators are simpler, with a one-line installation, and can be used in systems with multiple regulators. Nonetheless, they are not suitable for most EFI systems, can lead to increased fuel temperature, and may be hard on the fuel pump.

Bypass regulators improve performance and reliability

Bypass fuel pressure regulators improve performance and reliability in several ways. Firstly, they help keep the fuel cool by regulating the fuel to the required pressure and returning the excess fuel to the tank. This also eliminates "pressure creep", where fuel pressure slowly increases over time.

Bypass regulators also increase the life of the fuel pump and the regulator itself. This is because the fuel pump doesn't have to work as hard to maintain pressure, reducing the load on the pump and decreasing the voltage it uses. This also results in quieter pump operation.

Additionally, bypass regulators provide a more stable and smoother fuel pressure curve compared to deadhead fuel systems. This is because the supply of fuel is constantly circulating throughout the fuel system, allowing the bypass regulator to react more quickly to changes in engine load. This helps to keep the fuel bowls full, even during racing.

Overall, bypass fuel pressure regulators offer a more reliable and consistent setup, improving performance and extending the life of fuel system components.

Bypass regulators are a must for carbureted engines

First and foremost, they help maintain consistent fuel pressure. With deadhead regulators, fuel pressure can slowly creep up, leading to inconsistent fuel pressure numbers. In contrast, bypass regulators eliminate pressure creep by bleeding off excess fuel pressure and returning it to the fuel tank, ensuring a constant and stable fuel pressure.

Bypass regulators also improve the longevity of the fuel pump and regulator. In a deadhead system, the fuel pump hammers the regulator check valve, increasing fuel temperature and potentially leading to vapor lock. This additional strain shortens the lifespan of both the fuel pump and regulator. On the other hand, bypass regulators reduce the load on the fuel pump, increase its life, and decrease noise.

Additionally, bypass regulators enhance engine performance. They ensure that the fuel bowls remain full and reduce the chances of lean-out conditions, especially during racing. They also keep the fuel cool, which is crucial for optimal engine performance.

Furthermore, bypass regulators provide flexibility in plumbing arrangements. They can be mounted shortly after the carburetor, allowing fuel to flow through the carburetor before reaching the regulator. This setup requires stepping down the fuel line size before the carburetor, as using a large fuel line directly connected to the carb bowls is impractical.

Lastly, bypass regulators are easy to install and adjust. They only require the addition of a return line and can be fine-tuned using a threaded adjustment mechanism to control fuel pressure.

Overall, bypass regulators offer improved reliability, performance, and longevity for carbureted engines, making them a must-have upgrade.

Deadhead regulators are adjustable restrictions in the fuel line

Deadhead regulators are a type of blocking style fuel pressure regulator. They are adjustable restrictions in the fuel line that lower fuel pressure by decreasing fuel flow. Deadhead regulators are placed between the fuel pump and the carburetor, and they hold pressure at a steady 4.5 to 9 psi between the regulator and the carburetor. This setup works well for engines with lower horsepower, but it can struggle to maintain steady fuel pressure in high-output engines, leading to issues such as pressure creep, inconsistent fuel pressure, potential engine flooding, and heat.

The main issue with deadhead regulators is that they place an additional load on the fuel pump. As the fuel pump produces pressure, it hammers the regulator check valve, and the fuel has nowhere to go, leading to an increase in temperature. This can result in inconsistent fuel pressure, added fuel heat, and potential engine flooding. It can also shorten the life of both the fuel pump and the regulator.

In contrast, bypass regulators, also known as return-style regulators, bleed off excess fuel pressure and dump it into a return line, recirculating the fuel back into the tank. This helps keep the fuel cooler, eliminates pressure creep, and increases the life of the fuel pump and regulator.

Bypass regulators are more flexible and can be adapted to the needs of each application. For example, in a drag car, the regulator can be plumbed before the carburetor to build higher pressure in the feed, counteracting the g-forces during hard launches. In a street/strip application, the regulator can be placed on the return line side of the fuel log to allow unrestricted fuel flow to the carburetor while still regulating pressure and returning unused fuel to the tank.

Converting from a deadhead to a bypass regulator only requires adding two components: the bypass pressure regulator and a return line. This simple change offers a multitude of benefits in terms of reliability and performance.

Bypass regulators are ideal for fuel-injected applications

Bypass regulators offer several advantages over deadhead regulators in fuel-injected applications. Firstly, they improve fuel cooling by circulating fuel at a constant, lower pressure, reducing the load on the fuel system. This, in turn, increases the life of the fuel pump and regulator while also reducing noise. Secondly, they eliminate pressure creep, ensuring a smoother and more stable fuel pressure curve. This is particularly beneficial for race cars, as it enables the fuel system to react quickly to changes in engine load, reducing the chances of lean-out conditions on the race track.

Additionally, bypass regulators provide flexibility in plumbing arrangements. They can be mounted in a return line positioned shortly after the carburetor, allowing fuel to flow through the carburetor before reaching the regulator. This setup maintains fuel pressure regulation while providing the benefits of a bypass system. However, it is important to step down the fuel line size before the carburetor to ensure compatibility.

Bypass regulators are also beneficial in street/strip applications, where they can be positioned on the backside of the fuel log, allowing unrestricted fuel flow to the carburetor. This setup is ideal for drag cars with rear-mounted fuel tanks that experience hard launches. By plumbing the regulator before the carburetor, it is possible to increase line pressure during these intense acceleration events while still maintaining the desired fuel pressure at the carburetor.

In summary, bypass regulators offer enhanced reliability, consistency, and flexibility for fuel-injected applications. They improve fuel system performance and longevity by maintaining optimal fuel pressure, fuel temperature, and fuel flow, making them a preferred choice for fuel-injected cars, including street and race vehicles.

Returnless fuel systems don't need external return lines

Returnless fuel systems, also known as return-type fuel systems, are designed to use the powertrain control module (PCM) to regulate fuel delivery. They do not require external return lines, as the unused fuel is directed back into the tank after passing through a pressure regulator. This is in contrast to conventional return-type fuel systems, which pump excess fuel back to the tank via a return line.

The PCM in a returnless system monitors fuel pressure through a fuel pressure sensor mounted on the supply rail of the fuel injectors. If the fuel pressure and flow decrease due to increased engine speed or load, the PCM will compensate by increasing the injector duration and/or operating speed of the fuel pump. This ensures that the engine always receives the appropriate amount of fuel.

Returnless systems were introduced in the mid-1990s and have since become increasingly popular due to their ability to reduce the number of tank-to-engine trips to just one. This not only improves fuel efficiency but also helps to mitigate driveability issues caused by fuel evaporation, as in-tank fuel temperatures can exceed 160°F on hot days.

One drawback of returnless systems is the placement of the fuel filter, which can affect the system's longevity and ease of service and repair. If the filter is placed outside the tank, any unused fuel returned to the tank may contain contaminants that will repeatedly pass through the pump and back into the tank. On the other hand, placing the filter inside the tank makes it more difficult to replace. An optimal location for the filter is after the pressure regulator, allowing the unused fuel to be filtered repeatedly until it is used.

In summary, returnless fuel systems offer improved fuel efficiency and reduced fuel evaporation by eliminating the need for external return lines. However, careful consideration must be given to the placement of the fuel filter to ensure the longevity and serviceability of the system.

Frequently asked questions